Training of the abdominal set of muscles involves right activation of these muscles, while gradually bending the spinal backbone, preferably against controlled counter-force to allow controlled loading of these muscles. Only few devices for training the abdominal muscles are known which correctly lead the body of the user along a correct path of bending of the upper portion of the body. Most of these few devices are planned to use the user's own weight as a counter-force. None of these few devices is meant to be operated from a straight up position or a sitting position. Thus, when using most of the known devices, from a lay-down position the user has to overcome a substantially strong counter-power such as the user's own body weight. Yet for many users this is a limitation which may not be overcome, thus—such users are practically prevented from using the few known devices. Yet, training the abdominal muscles from a stand-up position without a counter-force against the bending body is almost useless, as the force required to be applied when the body bends down is substantially zero or even negative. If a training device known in the art is used, it will not lead the user's body to perform a correct bent trajectory as is required for the spinal backbone.